Minimally invasive spinal stabilization system

ABSTRACT

A spinal fixation assembly includes a pedicle rod and pedicle screws which secure the pedicle rod to the spine. Each pedicle screw includes a head configured to receive a portion of the pedicle rod, and a threaded portion extending from a first end of the head and configured to engage a vertebra. The pedicle rod is secured to the head by a fastener. The head includes a breakaway region that defines a location in which at least a first portion of the head can be easily separated from the remainder of the head upon application of sufficient force to the first portion. A minimally invasive method of implanting the spinal fixation assembly is disclosed.

BACKGROUND

Each year 13 million people see a doctor for chronic back pain, which isestimated to cause 2.4 million Americans to be chronically disabled.About 25 percent of people who have back pain have a herniated disk. Inthe US, about 450 cases of herniated disk per 100,000 require surgerysuch as a discectomy.

Referring to FIG. 1, a discectomy (FIG. 1( a)) is performed when theintervertebral disc 8 has herniated or torn and has not responded to amore conservative treatment. When a surgeon performs a discectomy, it isusually performed through an incision in the patient's back at alocation corresponding to the problem area of the spine 2. Muscles andligaments are moved aside to expose the offending disc 8. The surgeonthen uses a variety of surgical instruments to first separate thevertebrae 4 sandwiching the disc 8, and then remove the disc 8completely. After a discectomy is performed, the spinal column at theoperation site is separated to approximate the height of the removeddisc (FIG. 1 b), and then an artificial disk may be placed in theseparation. Spinal fixation devices (FIG. 1( c)) are used to stabilizeand/or align the spine 2 during the healing process following suchprocedures. In some cases, clinicians fill the separation with theimplantation of autologous bone to achieve fusion (fusion is illustratedin FIG. 1( d)) to restore stability of the spine 2. Alternatively,discectomy may be followed by spinal fusion, or other procedure that maybe deemed necessary to strengthen and straighten the spinal canal.

Although a discectomy is frequently performed using minimally invasivedevices and procedures, it is still challenging to provide the minimallyinvasive spine stabilization that is required following this and otherspinal procedures. Improved minimally invasive spinal fixation devicesand methods are required to minimizing patient risk, trauma, recoverytime, and to reduce the overall costs of such procedures.

SUMMARY

In some aspects, a minimally invasive spinal fixation assembly isprovided. The minimally invasive spinal fixation assembly is configuredto provide relative fixation of a series of vertebrae, and includes apedicle rod and pedicle screws, each screw including a head configuredto receive a portion of the pedicle rod, and a threaded portionextending from a first end of the head and configured to engage one ofthe vertebrae. The assembly further includes a fastener includingexternal threads configured to engage corresponding threads formed on aninner surface of the head. The pedicle rod is secured to the head by thefastener, and the head includes a breakaway region. The breakaway regionincludes a portion of the head that is formed to be relativelystructurally weak compared to the remaining portions of the head so asto define a location in which at least a first portion of the head canbe easily separated from the remainder of the head upon application ofsufficient force to the first portion.

The minimally invasive spinal fixation assembly may include one or moreof the following features: The pedicle rod is configured to engage asuture. The pedicle rod is a hollow tube. Each pedicle screw includesthe first end, and an open second end opposed to the first end. The headis generally tubular, and is formed of a single piece having a firstopening that extends from the second end along an axial direction of thehead to a location adjacent to, and spaced apart from, the first end,and a second opening on an opposed side of the body relative to thefirst opening, the second opening extending from the second end along anaxial direction of the body to a location adjacent to and spaced apartfrom the first end. The first and second openings are diametricallyaligned so as to form a transverse through channel through the head. Acap may be included that is configured to engage the second end of thepedicle screw head. The cap includes a hollow cylindrical body having anopen end dimensioned to receive therein a second end of the head, and anopposed end, the opposed end including a central cap opening. The firstend of the cap includes an interior surface having an annularprotrusion, and the head includes a circumferential groove adjacent tothe second end configured to engage the annular protrusion whereby thecap can be releasably secured to the second end of the head.

The minimally invasive spinal fixation assembly may include one or moreof the following additional features: A U-shaped pedicle screwstabilizer may be included. The stabilizer includes a grip portion, anannular base extending from one side of the grip portion and having adiameter substantially equal to the diameter of the head, and a pair oflegs extending from one side of the annular base, the legs configured toconform to the shape of, and be received within, the respective firstand second openings of the of the head. A cap may be included that isconfigured to close the second end of the pedicle screw head andincluding a cap opening through which the legs of pedicle screwstabilizer can be received. A portion of the edge of the capcorresponding to the cap opening is formed having a shape that conformsto a cross sectional shape of a leg. The minimally invasive spinalfixation assembly further includes a pedicle screw breaking deviceconfigured to be received within an interior space of the pedicle screwhead and facilitate separation of the second end of the head from thefirst end of the head along a prescribed circumferential breakaway lineprovided on the head between the first and second ends of the head.

The minimally invasive spinal fixation assembly may include one or moreof the following additional features: A suture guide assembly may beincluded. The suture guide assembly includes a suture leader configuredto retain a suture, and a guide tool including pivotably-joined firstand second arms. The first arm terminates at a first end in a malesuture guide, and the second arm terminates at a first end in a femalesuture guide. The male and female suture guides are configured to permitthe suture leader to be passed from the male suture guide to the femalesuture guide upon movement of the first and second arms between an openposition in which the male and female suture guides are spaced apart anda closed position in which the male and female suture guides areadjacent. The suture leader comprises a tip shaped to facilitateinsertion into the female suture guide, and an opening formed adjacentto the tip. The first and second arms are configured to be receivedwithin the hollow interior space of the pedicle screw head and passthrough the first and second openings. The series of vertebrae includesat least two vertebrae. The spinal fixation assembly is configured to beimplemented via non-continuous wound sites having a length generallycorresponding to a cross sectional dimension of the head.

In some aspects, a pedicle screw for use in spinal fixation is provided.The pedicle screw includes a head including a first end, and an opensecond end opposed to the first end, and a threaded body extending fromthe first end. The head is tubular, and is formed of a single piecehaving a first opening that extends from the second end along an axialdirection of the head to a location adjacent to, and spaced apart from,the first end, and a second opening on an opposed side of the bodyrelative to the first opening, the second opening extending from thesecond end along an axial direction of the body to a location adjacentto and spaced apart from the first end. The first and second openingsare diametrically aligned so as to form a transverse through channelthrough the head.

The pedicle screw may include one or more of the following features: Thedistance between first and second ends of the head is in a range from 40mm to 120 mm. The distance between first and second ends of the head isin a range from 50 mm to 80 mm. The head includes breakaway regionlocated between the first and second ends, the breakaway regionincluding a portion of the head that is formed to be relativelystructurally weak compared to the remaining portions of the head so asto define a location in which at least a portion of the second end canbe easily separated from the head upon application of sufficient forceto the second end. The breakaway region includes a circumferentialgroove positioned between the first end and a midpoint between the firstand second ends, the circumferential groove configured to provide aprescribed breakaway line along which at least a portion of the secondend can be easily separated from the head upon application of sufficientforce to the second end. The force is a twisting force about alongitudinal axis of the head. The pedicle screw further includes aremovable cap configured to close the head second end, wherein the headincludes a circumferential groove adjacent to the second end configuredto engage a corresponding annular lip provided on an interior surface ofthe cap. The first end of the head is configured to permit poly-axialrotation of the threaded body relative to the head.

In some aspects, a suture guide assembly is provided. The suture guideassembly includes a suture leader configured to retain a suture, and aguide tool including pivotably-joined first and second arms. The firstarm terminates at a first end in a male suture guide, and the second armterminates at a first end in a female suture guide. The male and femalesuture guides are configured to permit the suture leader to be passedfrom the male suture guide to the female suture guide upon movement ofthe first and second arms between an open position in which the male andfemale suture guides are spaced apart and a closed position in which themale and female suture guides are adjacent.

The suture guide assembly may include one or more of the followingfeatures: The suture leader includes a conical tip, and an eyeprotruding from the conical tip. The male suture guide includes acylindrical stem configured to releasably engage the suture leader eye,and the female suture guide includes cylindrical shell configured toreleasably engage the suture leader conical tip, and the guide tool isconfigured so as to support the male and female suture guides so thatthe conical tip at least partially received within the shell when theguide tool is in the closed position. The shell includes a first shellopening through which the suture leader is inserted into the shell, anda second shell opening through which the suture leader is withdrawn fromthe shell. The second shell opening has a shape that generally conformsto the shape of the suture leader. The first shell opening has adimension that is smaller than the dimension of the widest portion ofthe suture leader. The suture leader includes a conical tip, and whenthe guide tool is moved from the open position to the closed position,the conical tip of the suture leader is driven through the first shellopening, and is prevented from being retracted from the shell via thefirst shell opening. The first and second arms are angled. The arm angleis between 90-180 degrees.

In some aspects, a minimally invasive method for achieving spinalstabilization is provided. The method includes the following methodsteps: Implanting a pedicle screw into each vertebra of a portion of thespine to be stabilized, each pedicle screw implanted through a uniqueincision. Subcutaneously threading a suture through a correspondingpassage provided in each pedicle screw. Withdrawing a leading end of thesuture from the body through an access incision. Subcutaneouslythreading a hollow pedicle rod through the passage of each pedicle screwby passing the pedicle rod along the suture through the access incisioninto the body and through each respective passage such that the pediclerod spans all implanted pedicle screws. Securing the pedicle rodrelative to each pedicle screw.

The method may include one or more of the following additional stepsand/or features: At least two pedicle screws are implanted. Theimplanting step includes providing an incision through the skinoverlying the vertebra, where the incision length generally correspondsto the outer diameter of the pedicle screw; forming a hole in thepedicle; inserting a Kirshner pin at the desired implantation location;dilating soft tissues in the vicinity of the Kirshner pin; implant thepedicle screw in the hole of the vertebra by passing it along theKirshner pin and screwing the pedicle screw into the hole in thevertebra; and removing the Kirshner pin from the incision, leaving thepedicle screw in place. The step of threading a suture includes linkingthe pedicles screws by subcutaneously threading a suture through eachrespective pedicle screw head. The step of linking the pedicle screwsincludes the following: passing a suture through the interior space ofthe pedicel screw head from a second end of the pedicle screw head to afirst end of the screw head along a longitudinal axis of the pediclescrew head, the first end being closer to the spine than the second end;guiding the suture from the first end of the pedicle screw in adirection generally parallel to a longitudinal axis of the spine to thefirst end of an adjacent pedicle screw; withdrawing the suture from theadjacent pedicle screw head; and repeating the passing and guiding stepsfor the adjacent pedicle screw and any remaining pedicle screws. Priorto the step of threading a hollow pedicle rod, the following step isperformed: adjusting the curvature of the rod ex vivo and prior toinsertion into the body by bending the rod to correspond to thecurvature of a line defined by upper surfaces of the implanted pediclescrews. The securing step further comprises engaging exterior threads ofa set screw with corresponding threads provided on an interior surfaceof the pedicle screw such that the pedicle rod is retained between theset screw and the surface the pedicle screw. The pedicle screw includesa head including a first end, and a second end opposed to the first end,a threaded body extending from the first end, and an annular breakawayregion located between the first and second ends. The breakaway regionincludes a portion of the head that is formed to be relativelystructurally weak compared to the remaining portions of the head so asto define a location in which at least a portion of the second end canbe easily separated from the head upon application of sufficient forceto the second end. The securing step further comprises engaging exteriorthreads of a set screw with corresponding threads provided on aninterior surface of the pedicle screw head such that the pedicle rod isretained on the interior surface of the pedicle screw head at a locationbetween the first end and the breakaway region. The method furthercomprises the steps of removing a portion of the pedicle screw byapplying a force to the portion such that the portion breaks away fromthe remainder of the pedicle screw along a predetermined breakaway line.The force is a twisting force or a compressive force. The hollow pediclerod is at least 10 cm in length, and is inserted into the body throughthe access incision of up to about 1 cm in length. Each pedicle screw isimplanted through a unique incision of up to about 1 cm in length.

The minimally invasive spinal fixation device described herein can beimplanted through a series of small incisions of about 1 cm or lessalong the region of the spine to be supported. Advantageously, thisdevice avoids several drawbacks associated with many conventional spinalfixation devices. In particular, the minimally invasive spinal fixationdevice described herein does not need a large incision of 10 cm or morethrough which a spinal fixation cage can be implanted. As a result,patient risks of blood loss, infection, and/or tissue damage which canlead to lower back weakness can be avoided. In addition, recovery timeand negative side effects are minimized.

The spinal fixation device includes pedicle screws that secure a pediclerod to the respective vertebra within the region of the spine to bestabilized. Each pedicle screw includes a U-shaped head and a threadedportion that extends from one end of the head. The head is formed of anelongated single body having a circumferentially-extending, annularbreakaway region. In fact, the pedicle screw head has a sufficientlength to protrude upward out of the incision so as to permitmanipulation during implantation, and after implantation is complete,the excess length of the pedicle screw head can be broken off along thepre-defined breakaway region. Since the pedicle screw head ismanufactured as a single body, no preassembly of the screw head isrequired prior to implantation as is required in some conventionalpedicle screws, and there is no risk of malfunction or loss of smallcomponents into the wound site during implantation. Due to the fact thatthe pedicle screw head includes the breakaway region, removal of theexcess portions of the head after implementation is a very simple andquick procedure.

The method of implanting the spinal fixation device employs a novelmethod of threading a suture through a series of implanted pediclescrews, and then using the suture to link the pedicle screws using apedicle rod. This method is advantageous since it can be accomplishedperformed subcutaneously and submuscularly via minimal incisions.Moreover, the disclosed method permits a larger region of the spine tobe fixed than some known minimally invasive spinal fixation methods. Forexample, the method permits a series of four or more adjacent vertebrato be fixed.

Modes for carrying out the present invention are explained below byreference to an embodiment of the present invention shown in theattached drawings. The above-mentioned object, other objects,characteristics and advantages of the present invention will becomeapparent from the detailed description of the embodiment of theinvention presented below in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 (a)-1(d) illustrate procedures for repairing a herniated disk.

FIG. 2 is a perspective view of a minimally invasive spinal fixationsystem implanted on a series of four adjacent vertebrae.

FIG. 3 is a side view of a pedicle rod used in the spinal fixationsystem of FIG. 2.

FIG. 4 is an exploded perspective view of a pedicle screw assemblyincluding a pedicle screw as used in the spinal fixation system of FIG.2, a cap and a stabilizer tool.

FIG. 4 a is a cross-sectional view of the pedicle screw assembly of FIG.4, as seen across line 4 a-4 a.

FIG. 5 is a perspective view of a fastener used in the spinal fixationsystem of FIG. 2.

FIG. 6 a is an exploded view of a breaking tool used during implantationof the spinal fixation system of FIG. 2.

FIG. 6 b is an enlarged view of the portion of the breaking tool markedas 6 b in FIG. 6 a.

FIG. 6 c illustrates the breaking tool in use separating the pediclehead into two portions.

FIG. 7 is a perspective view of a guide tool assembly.

FIG. 8( a)-8(e) are alternative embodiments of a male suture guide ofthe guide tool assembly of FIG. 7.

FIG. 9( a)-9(d) are alternative embodiments of a female suture guide ofthe guide tool assembly of FIG. 7.

FIG. 10 is a side view of an awl used during implantation of the spinalfixation system of FIG. 2.

FIG. 11 is a detail view of the tip of the awl of FIG. 10.

FIGS. 12-14 illustrate use of the awl to form a pedicle screw hole andfacilitate insertion of a Kirshner pin into a vertebra.

FIG. 15 illustrates dilation of soft tissues in the vicinity of theKirshner pin.

FIG. 16 illustrates that the Kirshner pin remains in place aftercompletion of dilation and removal of the dilation tubes.

FIG. 17 illustrates insertion of the pedicle screw into the body overthe Kirshner pin.

FIGS. 18-19 illustrate implantation of the pedicle screw in thevertebra.

FIG. 20 illustrates repeating the pedicle screw implantation steps forseveral adjacent vertebrae.

FIG. 21 illustrates using a device to align the pedicle screw heads.

FIGS. 22-29 illustrate using the guide tool assembly to thread a suturesubcutaneously and submuscularly between respective first ends of theimplanted pedicle screw heads.

FIGS. 30-31 illustrate using the exposed ends of the pedicle screws as atemplate for preshaping the pedicle screw rod to the shape of the spineprior to implantation.

FIG. 32 illustrates threading the pedicle rod over the suture and acrossthe respective implanted pedicle screw heads.

FIG. 33 illustrates assembling a cap and stabilizer on the pedicle screwhead.

FIG. 34 illustrates insertion of a fastener through the cap andstabilizer to secure the pedicle rod to the pedicle screw.

FIG. 35 illustrates repeating the step shown in FIG. 34 for each pediclescrew.

FIGS. 36-37 illustrate using the breaking tool to break off a dorsalportion of each pedicle screw head.

FIG. 38 illustrates the implanted spinal fixation system.

FIG. 39 is a perspective view of another embodiment of a guide toolassembly.

DETAILED DESCRIPTION

Referring to FIG. 2, a minimally invasive spinal fixation system 20 usedto stabilize a region of the spine 2 includes a fixation rod 200 ofsufficient length to extend across the vertebrae 4 to be stabilized,pedicle screws 300 for anchoring the fixation rod 200 to eachcorresponding vertebra 4, and a fastener 500 on each pedicle screw 300to secure the pedicle rod 200 to the pedicle screw 300. Each pediclescrew 300 is implanted in the pedicle 6 of the corresponding vertebra 4through a small skin incision having a length generally corresponding toa cross sectional dimension of the pedicle screw 300. In the illustratedembodiment, for example, the incision has a length of 1 cm or less, andthe rod 200 is assembled with the pedicle screws 300 through a separateskin incision of 1 cm or less, as discussed further below.

Referring to FIG. 3, the fixation rod 200 is a structure that isconfigured to engage a suture, where a suture is defined herein as anelongated strand or fiber such as a thread or wire. In the illustratedembodiment, the fixation rod 200 is a hollow tube, including a first end212, a second end 214 that is opposed to the first end 212, and aninterior passageway 210 that extends between the first end 212 and thesecond end 214. In this embodiment, the fixation rod 200 can receive asuture within the passageway 210.

The rod 200 is relatively long compared to its cross-sectionaldimension. For example, in the illustrated embodiment, the rod 200 iscylindrical, and it has a diameter of 5.5 mm and an axial length thatcorresponds to the overall length of the region of the spine 2 to bestabilized. For example, to stabilize two adjacent vertebrae 4, the rodhas a length of approximately 60.0 mm. To stabilize a series of fouradjacent vertebrae 4, the rod has a length of approximately 150.0 mm.The rod 200 is formed of an implantable material, and is formed of amaterial of sufficient strength and stiffness to provide spinalstabilization, while also being sufficiently malleable to permit shapingof the rod curvature. For example, the rod 200 may be formed of atitanium alloy such as Ti6Al4V.

Referring to FIG. 4, a polyaxial pedicle screw 300 is used to anchor thepedicle rod 200 to each corresponding vertebra 4. Each pedicle screw 300is dimensioned to be inserted through a skin incision of 1 cm or lessand screwed into the pedicle of the corresponding vertebra 4, which liesbelow the skin and underlying muscle at a depth of about 5 cm for anaverage male. Toward this end, each pedicle screw 300 includes anelongated head 302 and a threaded tip 304.

The head 302 is generally tubular, and is formed of a single piece. Thehead 302 includes a closed first end 306, and an open second end 308that is opposed to the first end 306. The head 302 is provided with afirst axially-extending opening 310 that extends from the second end 308to a location adjacent to, and spaced apart from, the first end 306. Thehead 302 is also provided with a second axially-extending opening 312 onan opposed side of the head 302 relative to the first opening 310.Mirroring the first opening 310, the second opening 312 extends from thesecond end 308 to a location adjacent to and spaced apart from the firstend 306. The first and second openings 310, 312 are diametricallyaligned so as to form a transverse through channel 316 through the head302. As a result, the head 302 is generally U shaped.

The head 302 is long in an axial direction relative to its crosssectional dimension. For example, in the illustrated embodiment, thedistance d1 between the first end 306 and the second end 308 is in arange from 4 cm to 12 cm, whereas it has a diameter of about 1 cm. Inother embodiments, the distance d1 may be in a range of 5 cm to 8 cm.

The head 302 is provided with an annular breakaway region 318 that islocated between the first end 306 and the second end 308. In theillustrated embodiment, the breakaway region 318 is located between thefirst end 306 and a midpoint P between the first and second ends 306,308, or more specifically, at a location about midway between the pointP and the first end 306. As a result, the head 302 is partitioned intotwo portions by the breakaway region 318. A ventral portion 322 thatextends between the first end 306 and the breakaway region 318; and adorsal portion 324 that extends between the breakaway region 318 and thesecond end 308. The breakaway region 318 is a region of the head 302that is formed to be relatively structurally weak compared to theremainder of the head 302 so as to define a circumferential line alongwhich the dorsal portion 324 can be easily separated from the ventralportion 322 upon application of sufficient force to the dorsal portion324. In the illustrated embodiment, the breakaway region 318 is acircumferentially-extending V-shaped groove 320. In some embodiments,the spinal fixation system 20 may include a screw breaking tool 800,described further below, that is configured to provide a twisting forceabout a longitudinal axis of the head 302 and thereby selectivelyseparate the dorsal portion 324 from the ventral portion 322 at thegroove 320. It will be appreciated that although a bending force couldalso be applied to the dorsal portion 324 to achieve separation, use ofa twisting force will be less damaging to surrounding tissues than abending force.

The interior surface of the ventral portion 322 is provided with threads326 configured to engage corresponding threads 508 provided on an outersurface 506 of a fastener 500, described further below. In addition, aretention groove 332 is formed in the outer surface of the head 302 at alocation adjacent the second end 308. The retention groove 332 isdimensioned and positioned so as to receive and retain a correspondingannular ridge 610 formed on an inner surface of a screw cap 600,described further below.

The threaded tip 304 of the pedicle screw 300 extends outward from thefirst end 306 of the head 302. More specifically, the threaded tip 304includes a base 342 that is supported within the first end 306 of thehead 302, and a shank 344 that extends from the base. The first end 306of the head 302 is configured to permit three dimensional rotation ofthe threaded tip 304 relative to the head 302. The shank 344 has outerthreads and terminates at an apex 346. In addition, the threaded tip 304includes an axial through hole 350 that opens at the base 342, extendsthrough the shank 344 and opens the apex 346.

Referring to FIG. 5, the fastener 500 is a cylindrical member havingexternal threads 508 formed on an outer surface 506. The threads 508 areconfigured to engage corresponding threads 326 formed on an innersurface of the ventral portion 322 of the pedicle screw head 302. In theillustrated embodiment, the fastener 500 is a set screw having a firstend 502 that is configured to receive a driving tool. For example, theend 502 includes a hexagonal-shaped socket 510 suited for receiving ahex wrench, or the shaped tip 892 of an actuator tool 850 (describedbelow). In use, the fastener 500 is secured to the ventral portion 322of the pedicle screw head 302 so as to retain the position of thefixation rod 200 relative to the pedicle screw 300.

Referring again to FIG. 4, the spinal fixation system 20 furtherincludes a removable screw cap 600 that is shaped and dimensioned to besecured to the pedicle screw head second end 308, to support andstabilize the head second end 308, and to serve as a guide to direct astabilizer tool 700 (described below) during insertion of the stabilizertool 700 into the hollow interior of the pedicle screw 300 (describedbelow). The screw cap 600 is a hollow cylinder having an open first end602, a closed second end 604 opposed to the first end 602, and asidewall 606 extending between the first end 602 and the second end 604.The open first end 602 is dimensioned to receive the second end 308 ofthe pedicle screw head 302 therein.

The screw cap sidewall 606 is provided with a first axially-extendingcap opening 612 that extends from the first end 602 to a locationadjacent to, and spaced apart from, the second end 604. The screw capsidewall 606 is also provided with a second axially-extending capopening 614 on an opposed side of the sidewall 606 relative to the firstcap opening 612. Mirroring the first cap opening 612, the second capopening 614 extends from the first end 602 to a location adjacent to andspaced apart from the second end 604. The first and second cap openings612, 614 are diametrically aligned so as to form a transverse throughchannel 616 through the screw cap 600. When the screw cap 600 isdisposed on the second end 308 of the pedicle screw head 302, the screwcap transverse through channel 616 can be aligned with the pedicle screwthrough channel 316.

The screw cap 600 includes an inwardly-protruding annular ridge 610formed on an interior surface of the sidewall 606 that is sized andpositioned to permit engagement with the cap retention groove 332 formedon the pedicle screw second end 608. The protruding ridge 610 extendsabout the inner circumference of the sidewall, and cooperates with theretention groove 332 to maintain the screw cap 600 on the pedicle screwsecond end 308.

In addition, the second end 604 of the screw cap 600 includes a centralopening 618. The central opening 618 has an irregular shape, including agenerally circular central portion 622 and an elongated portion 624positioned along each opposed side of, and intersecting, the centralportion 622. In the illustrated embodiment, the central portion 622 isshaped and dimensioned to permit passage of surgical tools through thescrew cap 600 and into the interior space of the pedicle screw head 302.In addition, the elongated portions 624 are shaped and dimensioned toreceive leg portions 712 of the stabilizer tool 700 when the stabilizertool 700 is inserted into the hollow interior of the pedicle screw 300(described below). It should be noted that the elongated portions 624 ofthe central opening 618 are located along a periphery of the second end604 so as to overlie respective first and second cap openings 612, 614.This configuration ensures that the leg portions 712 of the stabilizertool 700 are aligned with respective first and second openings 310, 312of the pedicle screw head 302 after assembly of the pedicle screw 300,cap 600 and stabilizer tool 700, as discussed further below.

The spinal fixation system 20 further includes the stabilizer tool 700which is a hollow cylinder including an open first end 702, a closedsecond end 704 opposed to the first end 702, and a sidewall 706extending between the first end 702 and the second end 704. The sidewall706 is formed having an outer diameter that corresponds to that of thepedicle screw head 302 and diametrically opposed openings 708, 710 thatextend axially from the first end 702 to a location adjacent the secondend 704. The openings 708, 710 provide the sidewall 706 with a generallyU-shape, including leg portions 712 that are joined by an annular baseportion 714. A grip portion 716 is disposed between the base portion 714and the second end 704 that has a larger outer diameter than the baseportion 714, and includes surface features such as axially-extendinggrooves 718 to improve gripability. In addition, the second end 704includes a central opening (not shown in FIG. 4) through which tools canbe inserted.

When the stabilizer tool 700 is assembled with the cap 600 and pediclescrew 300, the leg portions 712 reside within the openings 310, 312 ofthe pedicle screw head 302 (see FIG. 4 a). The stabilizer tool 700 isused to position the pedicle rod 200 within the interior space of thepedicle screw head 302 during implantation of the spinal fixation system20. In addition, the stabilizer tool 700 is used to maintain theposition of the pedicle rod 200 while the fastener 500 is used to securethe pedicle rod 200 to the ventral portion 322 of the pedicle screw head302, and to reinforce the dorsal portion 324 during separation of thedorsal portion 324 from the ventral portion 322 after implantation, asdiscussed further below.

Referring to FIGS. 6 a-6 c, the spinal fixation system 20 furtherincludes the screw breaking tool 800 that is configured to be receivedwithin the interior space of the pedicle screw head 302 and is used toremove the dorsal portion 324 of the pedicle screw head 302 once thepedicle screw ventral portion 322 and pedicle rod 200 are correctlypositioned and mutually fixed. The screw breaking tool is 800 includes asleeve 820 and a T-shaped actuator 850 shaped and dimensioned to bereceived within the sleeve 820 (FIG. 6 a). The sleeve 820 is a hollowcylinder that includes an open first end 802, a second end 804 opposedto the first end 802, and a sidewall 806 extending between the first end802 and the second end 804. A pair of slots 814 (only one slot 814 isshown) extend from the first end 802 toward a mid portion of the sleeve820. The slots 814 divided the first end 802 into two end portions 802a, 802 b. A grip region 810 is provided on the second end 804 that has alarger outer diameter than the sidewall 806, and includes surfacefeatures such as axially-extending grooves 818 to improve gripability.In addition, the second end 804 includes a central opening 812 throughwhich tools, including the actuator 850, can be inserted. The axiallength of sleeve 820 is greater than that of an assembly of the pediclescrew 300, cap 600 and stabilizer tool 700.

The actuator 850 includes a shank 854 having a first end 856 and asecond end 858. A handle 852 is fixed to the second end 858, giving theactuator its T-shape. The shank first end 856 includes a flared portion890, and a shaped portion 892 that extends coaxially from the flaredportion 890 (FIG. 6 b). The shaped portion 892 has an outer crosssectional dimension that is less than that of the flared portion 890 andshank 854, and includes surface features that enable it to engage thesocket 510 of the fastener 500. For example, in the illustratedembodiment, the shaped portion 892 is hexagonal in cross-sectional shapeso as to engage the hexagonal socket 510 of the fastener 500. The flaredportion 890 has an outer dimension that is greater than that of thesleeve sidewall 806 and the diameter of the interior space of thepedicle screw head 302. When the actuator 850 is assembled within thesleeve 820 with the flared portion 890 protruding beyond the sleevefirst end 802, the sleeve 820 can be inserted into the screw head 302,for example to secure the fastener 500 to the screw head 302. By drawingthe actuator 850 upward so that at least a portion of the flared portion890 is disposed within first end of the sleeve 820, the flared portion890 causes the two end portions 802 a, 802 b to slightly separate. Bythis action, the outer wall of the sleeve 820 is compressed against theinner wall of the pedicle screw head dorsal portion 324. Due tofrictional engagement of the sleeve 820 with the pedicle screw head 302,by rotating the actuator 850 about its longitudinal axis, a twistingforce is applied to the dorsal portion 324 of the screw head 302. Uponapplication of sufficient force, the dorsal portion 324 of the screwhead 302 can be separated from the ventral portion 322 along thebreakaway line 318 (FIG. 6 c).

Referring to FIG. 7, a suture guide assembly 900 is used to implant thepedicle rod 200 within each respective pedicle screw head 302, asdiscussed further below. The suture guide assembly 900 includes a guidetool 980 having a pair of elongated arms 982, 984 that are joined via apivot pin 986 at a location between respective arm first ends 988 andrespective arm second ends 990. The first end 988 of each arm 982, 984is formed into a finger loop 992 to permit manual actuation of the tool,and the second end 990 of each arm 982, 984 is configured to hold asuture guide 940, 960. During actuation, the arms 982, 984 of the guidetool 980 move in a scissoring motion about the pin 986.

The first and second arms 982, 984 of the guide tool 980 are eachdimensioned to be received within the hollow interior space of thepedicle screw head 302 and to extend along the axial length of thepedicle screw head 302. Moreover, the guide tool 980 operates in ascissoring motion in which the first arm 982 and the second arm 984 movebetween an open position (shown in FIGS. 7 and 22-23) in which thesecond ends 990 of the arms 982, 984 are spaced apart a first distance,and a closed position in which the second ends 990 of the arms 982, 984are spaced apart a second distance (shown in FIG. 24), the firstdistance being greater than the second distance. The first and secondarms 982, 984 are dimensioned to pass through the pedicle screw headfirst and second openings 310, 312 when the guide tool 980 is actuatedwhile the guide tool 980 is inserted in a pedicle screw 300, asdiscussed further below. In some embodiments, the first and second arms982′, 984′ can be angled. For example, the arms 982′, 984′ may be angledmidway between the pivot pin 986′ and the arms second ends 990′, so thatthe second ends 990′ lie out of a plane defined by the finger loops 992′(FIG. 39). The arm angle may be in a range between 90-180 degrees.

The suture guide assembly 900 also includes a leader 920 that retains anend of a suture 1216 (not shown in FIG. 7), a male suture guide 940mounted on the first arm 982 of the guide tool 980, and a female sutureguide 960 mounted on the second arm 984 of the guide tool 980.

Referring to FIG. 7, detail A, the leader 920 includes a conical tip 922having an apex 926. In addition, the leader 920 includes an eyelet 924protruding from the tip 922 on a side 928 opposite to the apex 926. Thediameter of the eyelet 924 is small relative to the diameter of the side928. In use, a suture 1216 is secured to the leader 920 using the eyelet924, as discussed further below.

The male suture guide 940 includes a base 946 that is received in andsupported by the second end 990 of the guide tool arm 982, and acylindrical stem 942 extending from an axial end of the base 946. Thestem 942 is configured to releasably engage the leader eyelet 924. Inparticular, the stem 942 includes an axially extending opening 948dimensioned to receive the eyelet 924 in a press fit manner. The stem942 also includes a transverse opening 950 that extends through adiameter of the stem 942 in a direction transverse to the axial opening948 and intersects the axial opening 948. Thus, when the eyelet 924 ofthe leader 920 is received within the axial opening 948 with a suture1216 attached thereto, the suture 1216 passes freely along thetransverse opening 950 without binding and a portion of the suture 1216drapes outward from the transverse opening 950.

Referring to FIG. 7, detail B, the female suture guide 960 includes abase 968 that is received in and supported by the second end 990 of theguide tool arm 984, and a hollow cylindrical shell 962 extending from anaxial end of the base 968. The shell 962 is configured to receive theleader 920 from the male suture guide 940, and to releasably retain theconical tip 922 therein. In particular, the shell 962 includes a firstshell opening 966 through which the conical tip 922 of the leader 920 isinserted into the hollow interior of the shell 962, and a second shellopening 964 through which the leader 920 is withdrawn from the shell962. The first shell opening 966 is located on an axial end of the shell962, is generally circular in shape and has a dimension that is smallerthan the dimension of the leader side 928. The second shell opening 964is located on a sidewall of the shell 926, and has a shape thatgenerally conforms to the size and shape of the tip 922 of the leader920. In the illustrated embodiment, the second shell opening 964includes a triangularly shaped portion through which the leader 920,including the conical tip 922, can be withdrawn from the shell 962.

In use, the suture leader is supported on a first arm 982 of the guidetool 980, and particular is retained in the axial opening 948 of thestem 942 of the male suture guide 940. The male suture guide 940 isconfigured to support the leader 920, and to transfer the leader 920 tothe female suture guide 960 upon movement of the first arm 982 and thesecond arm 984 to the guide tool closed position. In the closedposition, the male suture guide 940 and female suture guide 960 aretouching or nearly touching. As a result, the leader 920, which isdisposed on a side of the male suture guide 940 that faces the femalesuture guide 960, is pressed into the female suture guide 960. Inparticular, as the guide tool 980 moves to the closed position, the tip922 is inserted, apex 926 first, into the first shell opening 966.Although the first shell opening 966 is small relative to the outerdimensions of the leader end 928, the shell 962 is formed to berelatively structurally weak so that the tip 922 of the leader 920 canpass through the first shell opening 966. Due to the size differencesbetween the first shell opening 966 and the tip side 928, the leader 920is prevented from being withdrawn from the shell 962 through the firstopening 966. The leader 920, housed within the shell 962 of the femalesuture guide 960, is now retained on the second end 990 of the secondarm 984 of the guide tool 980, and moves with the second arm 984 whenthe guide tool 980 is opened. Thus, by using the guide tool 980, asuture 1216 can be secured to the first arm 982 by attaching a leader920 to the male suture guide 940, and the suture 1216 can then passed tothe second arm 984 via the female suture guide 960 through a simpleoperation of the guide tool 980. Since the guide tool arms 982, 984 areconfigured to fit within the pedicle screw heads 302, and because thepedicle screw heads 302 each include axially-elongated side openings310, 312, a suture 1216 can be passed subcutaneously and submuscularlybetween adjacent pedicle screws 300 after implantation of the pediclescrews 300 in the spine. This feature is important to the method ofusing the system 20, as discussed further below.

Referring to FIGS. 8( a)-8(e), some examples of alternative embodimentmale suture guides 1340 are illustrated. For example, in FIG. 8( a), themale suture guide 1340 a may be formed integrally with the sutureleader, and includes a base 1346 a that is configured to be supported onthe second end of the guide tool arm 982, the base 1346 a including anopening 1342 a to which a suture can be secured. The male suture guide1340 a also includes a conical tip 1322 a to facilitate insertion intothe corresponding opening of the female suture guide 960. FIGS. 8( b) to8(e) illustrate additional alternative embodiments of the male sutureguide, where like reference numbers refer to like structures. In thesealternative embodiments, it can be seen that the base 1346 can be formedhaving a larger outer diameter than the tip 1322 (FIG. 8( b)) or formedhaving a non-cylindrical shape (FIGS. 8( b), 8(d), 8(e)). In addition,the tip 1322 is not limited to having a conical shape (FIGS. 8( b),8(c), 8(d)).

Referring to FIGS. 9( a)-9(d), examples of alternative embodiment femalesuture guides 1360 are illustrated. For example, in FIG. 9( a), thefemale suture guide 1360 a includes a base 1362 a that is configured tobe supported on the second end of the guide tool arm 984. In thisexample, the base 1362 a also serves as the shell portion and includes afirst shell opening 1366 a through which the leader tip 922, 1322 isinserted into the hollow interior of the base 1362 a, and a second shellopening 1364 a through which the leader 920 is withdrawn from the base1362 a. FIGS. 9( b) to 9(d) illustrate additional alternativeembodiments of the female suture guide 1360, where like referencenumbers refer to like structures. In these alternative embodiments, itcan be seen that the first shell opening 1366 and second shell opening1364 may be formed having different shapes (FIGS. 9( b), 9(c), 9(d)),for example to compliment a corresponding structure of the male sutureguide and/or facilitate insertion and/or extraction of the leader fromthe female suture guide 1360.

Referring to FIGS. 10 and 11, an awl 1400 is used to prepare eachvertebra for implantation, as described further below. The awl 1400includes an elongated shaft 1402 that terminates at one end in a handle1420 and at the other end with a cutting tip 1408. The cutting tip 1408has a drill portion 1416 on a leading end thereof, and a tap portion1414 disposed between the drill portion 1416 and the shank 1402. Inaddition, an axially extending through hole 1418 that extends from thehandle 1420 to the cutting tip 1408 is dimensioned to receive a Kirshnerpin 1200.

Referring to FIGS. 12-39, an example of a minimally invasive method forachieving spinal stabilization using spinal fixation system 20 will nowbe described.

In Step 1, a pedicle screw 300 is implanted into each vertebra 4 of aportion of the spine 2 to be stabilized (FIGS. 12-20). Implantation ofpedicle screws 300 includes the following:

-   -   Step 1 a. Provide an incision through the skin 10 overlying the        vertebra 4. In general, the incision length corresponds to the        outer diameter of the pedicle screw 300, and may be slightly        less due to the pliability of skin. In the illustrated        embodiment, the pedicle screw 300 is approximately 1 cm in        diameter, whereby an incision of at most 1 cm is required to        accommodate pedicle screw 300.

Step 1 b. Referring to FIG. 12, prepare the vertebra 4 to receive thepedicle screw 300 by forming a threaded hole in the pedicle 6. An awl1400 (described in co-pending U.S. applications having Ser. Nos.13/161,705 and 13/161,698 and incorporated by reference herein) isinserted into the incision and is used to locate the pedicle and formthe threaded hole therein. Correct positioning is verified using animaging device such as a C-arm or fluoroscope.

-   -   Step 1 c. Referring to FIG. 13, insert a Kirshner pin 1200        through the axial passageway 1418 of the awl and into the        vertebra 4 at the desired implantation location.    -   Step 1 d. Referring to FIG. 14, removal the awl 1400, leaving        the pin 1200 in place.    -   Step 1 e. Referring to FIGS. 15-16, insert a series of dilation        cannulas 1202, 1204 into the incision over the pin 1200,        starting with a relatively small-diameter cannula 1202, and each        successive cannula having a slightly larger outer diameter.        Although only two cannulas 1202, 1204 are shown, six to eight        cannulas may be used in order to dilate the skin 10, muscle and        other soft tissues in the vicinity of the pin 1200 and create        space for insertion of the pedicle screw 300 into the body (FIG.        15). The pin 1200 is used to stabilize and direct each        respective dilation cannula 1202, 1204 during dilation. After        dilation is completed, the dilation cannulas 1202, 1204 are        withdrawn, leaving the pin 1200 in place (FIG. 16).    -   Step 1 f. Referring to FIGS. 17-18, implant the pedicle screw        300 in the pre-threaded drill hole of the vertebra 4 by passing        it along the pin 1200. Specifically, the pedicle screw 300 is        loaded onto the pin 1200 so that the pin 1200 is received within        the shank axial through hole 350 and the interior space of the        pedicle screw head 302. The pin 1200 serves to stabilize and        direct the pedicle screw shank 344 so that the threads 348 on        the shank 344 engage with and are screwed onto the drill hole        threads. In the illustrated embodiment, a driving tool is used        to rotate the pedicle screw 300, screwing the pedicle screw into        the hole in the vertebra 4. As seen in the figure, when the        shank 344 is fully screwed into the vertebra 4, a portion of        pedicle screw head 302 protrudes through the incision outwardly        relative to the skin 10.    -   Step 1 g. Referring to FIG. 19, remove driving tool and pin 1200        from the incision, leaving the pedicle screw 300 in place.    -   Step 1 h. Referring to FIG. 20, repeat the previous pedicle        screw 300 implantation steps 1 a-1 g for each vertebra 4 to be        stabilized. In the illustrated embodiment, four vertebrae 4 are        to be stabilized, whereby a pedicle screw 300 is implanted in        each of the four vertebrae 4 (300 a, 300 b, 300 c, 300 d).

Referring to FIG. 21, Step 2 includes aligning the respective pediclescrew heads 302 using an alignment tool 1214 so that the longitudinalaxes of the screws 300 are parallel to each other and verticallyaligned. In FIG. 21, a reference frame is defined in which an x axiscorresponds generally to a longitudinal axis of the spine 2 and isoriented horizontally, and a y axis transverse to the x axis is orientedvertically and corresponds to an anterior-posterior direction of thespine 2. In step 2, the respective pedicle screw heads 302 are alignedso that the first and second pedicle screw openings 310, 312 open alongthe x axis, and thus the respective pedicle screw transverse openings318 are aligned with the x axis.

Step 3 includes linking the pedicles screws 300 by subcutaneouslythreading a suture 1216 through the respective pedicle screw heads 302.Linking the pedicle screws 300 includes the following:

-   -   Step 3 a. Referring to FIGS. 22-23, use the suture guide tool        980 to insert a suture 1216 into the cranial-most pedicle screw        300 a such that the suture leading end passes through the        interior space of the pedicel screw head 302 from the second end        308 of the head to the first end 306 (e.g., along the y axis).    -   Step 3 b. Referring to FIGS. 24-25, actuate the guide tool 980        to guide the suture 1216 from the first end 306 of the        cranial-most pedicle screw 300 a to the first end 306 of the        adjacent pedicle screw 300 b along the x axis and generally        parallel to the longitudinal axis of the spine 2. In particular,        the suture 1216 is transferred between adjacent pedicle screws        300 a, 300 b by actuating the guide tool 980 from an open        position to a closed position, whereby the leader 920 is        transferred from the male suture guide 940 to the female suture        guide 960 (FIG. 24). The suture 1216 is then moved to the        adjacent pedicle screw 300 b by actuating the suture guide to an        open position (FIG. 25).    -   Step 3 c. Referring to FIG. 26, the suture guide tool 980 is        withdrawn from the pedicle screw heads 302 a, 302 b, with the        suture 1216 now linking the cranial-most pedicle screw 300 a and        the adjacent pedicle screw 302 b. At this time, the leader 920        is transferred back to the male suture guide 940, in preparation        for repeating steps 3 a and 3 b for pedicle screws 300 b and 300        c.    -   Step 3 d. Referring to FIG. 27, Steps 3 a-c are repeated until        the first end 306 of each pedicle screw 300 a, 300 b, 300 c, 300        d is serially linked subcutaneously and submuscularly via the        suture 1216. Although the linking step is described as        proceeding from the cranial-most pedicle screw 300 a to the        caudal-most pedicle screw 300 d, the method is not limited to        this. For example, the method can include proceeding from        caudal-most to cranial-most pedicle screw 300.

Step 4 includes withdrawing the suture leading end 1216 a from the bodythrough a small access incision (1 cm or less) located caudally withrespect to the caudal-most pedicle screw 300 d. Withdrawing the sutureincludes the following:

-   -   Step 4 a. Referring to FIGS. 28-29, a compass tool 1218 is        provided that facilitates withdrawal of the suture 1216 from the        body. The compass tool 1218 includes a base leg 1220 configured        to hold the suture leader 920 and a curved pivoting leg 1222        configured to receive the suture leader 920, and to pivot        relative to the base leg 1220 about a pivot axis at one end of        the base leg 1220. As seen in FIG. 28, the base leg 1220 holds        the suture leader 920 adjacent the pedicle screw 300 d. In        subsequent actions, the base leg 1220 is inserted into the        caudal-most pedicle screw 300 d, and the pivoting leg 1222 is        rotated (clockwise in the figure) relative to the base leg 1220        so as to pass through the access incision. As a result, the        suture leader 920 is moved from an end of the base leg 1220 to        an end of the pivoting leg 1222 in a manner similar to that used        within the suture guide assembly 900. The pivoting leg 1222 is        then rotated (counterclockwise in the figure) relative to the        base leg 1220 to withdraw the suture 1200 from the access        incision (FIG. 29).

Referring to FIGS. 30 and 31, Step 5 includes providing a pedicle rod200. In particular, the pedicle rod 200 must be provided in a lengththat is at least sufficient for the rod to simultaneously span allimplanted pedicle screws 300 a-300 d. In some embodiments, therespective protruding second ends 308 of the pedicle screws 300 may beused as a template to cut a length of rod stock to the desired length(FIG. 30). In addition, the pedicle rod 200 is preformed to have acurvature (shown as a dashed line) corresponding to the curvature of thespine 2. In particular, the curvature of the pedicle rod 200 is adjustedex vivo and prior to insertion into the body by bending the rod 200 tocorrespond to the curvature of a line defined by the upper surfaces ofthe second ends 308 of the implanted pedicle screws 300 (FIG. 31).

Referring to FIG. 32, Step 6 includes subcutaneously and submuscularlythreading the sized- and shaped-pedicle rod 200 onto the suture 1216 bypassing the suture 1216 through hollow interior passageway 210 of thepedicle rod 200.

Step 7 includes passing the pedicle rod 200 along the suture 1216 intothe body and through each respective pedicle screw head 302 such thatthe pedicle rod 200 resides in the transverse passage 316 adjacent thefirst end 306 of each respective pedicle screw head 302.

Step 8 includes removing the suture 1216 from the body, leaving thepedicle rod 200 in position within the series of pedicle screws 300.

Step 9 includes securing the pedicle rod 200 to each pedicle screw 300.The following steps are used to secure the pedicle rod 200 to a pediclescrew:

-   -   Step 9 a. Referring to FIG. 33, stabilize the pedicle rod 200        with respect to the pedicle screw 300 by securing the cap 600 to        the pedicle screw head second end 308, and then inserting the        stabilizer tool 700 through the cap and onto the pedicle screw        head 302. When assembled, the stabilizer tool legs 712 securely        seat the pedicle screw rod 200 within the interior space of the        pedicle screw head 302 at the lowermost aspect of the first and        second openings 310, 312, and maintain the rod 200 in that        position during the subsequent step (9 b).    -   Step 9 b. Referring to FIG. 34, secure the pedicle rod 200        relative to the pedicle screw 300 by using the actuator 850 to        drive the set screw 500 into the pedicle screw head 302 such        that the exterior threads 508 of the set screw 500 engage with        corresponding threads 326 provided on the interior surface of        the first end 306 of the pedicle screw head 302. As a result,        the pedicle rod 200 is retained between the set screw 500 and        first end 306 of the pedicle screw 300.    -   Step 9 c. Referring to FIG. 35, repeat steps 9 a and 9 b until        the pedicle rod 200 is secured to each pedicle screw 300 a-300        d.

Step 10 includes removing the pedicle screw head dorsal portion 324 fromthe remainder of the head 302 of each pedicle screw. The removing stepincludes the following:

-   -   Step 10 a. Referring to FIGS. 36-38, apply a twisting force to        the dorsal portion 324 using the breaking tool 800 such that the        dorsal portion 324 breaks away from the first end of the pedicle        screw along the annular breakway region 318, and withdrawing the        separated dorsal portion 324 from the body.

Step 11 includes closure of all minimal incisions.

A selected illustrative embodiment of the invention is described abovein some detail. It should be understood that only structures considerednecessary for clarifying the present invention have been describedherein. Other conventional structures, and those of ancillary andauxiliary components of the system, are assumed to be known andunderstood by those skilled in the art. Moreover, while a workingexample of the present invention has been described above, the presentinvention is not limited to the working example described above, butvarious design alterations may be carried out without departing from thepresent invention as set forth in the claims.

What is claimed is:
 1. A suture guide assembly including a suture leaderhaving a conical tip and an eyelet protruding from the conical tip, theeyelet having an opening transverse to a longitudinal axis of theconical tip and configured to retain a suture, and a guide toolincluding pivotably-joined first and second arms, the first armterminating at a first end in a male suture guide, the second armterminating at a first end in a female suture guide, wherein the maleand female suture guides are configured to permit the suture leader tobe passed from the male suture guide to the female suture guide uponmovement of the first and second arms between an open position in whichthe male and female suture guides are spaced apart at least a distancebetween two adjacent vertebrae and a closed position in which the maleand female suture guides are adjacent.
 2. The suture guide assembly ofclaim 1, wherein the male suture guide includes a cylindrical stemconfigured to releasably engage the suture leader eye, and the femalesuture guide includes a cylindrical shell configured to releasablyengage the suture leader conical tip, and the guide tool is configuredso as to support the male and female suture guides so that the conicaltip is at least partially received within the shell when the guide toolis in the closed position.
 3. The suture guide assembly of claim 2wherein the shell includes a first shell opening through which thesuture leader is inserted into the shell, and a second shell openingthrough which the suture leader is withdrawn from the shell.
 4. Thesuture guide assembly of claim 3 wherein the second shell opening has ashape that generally conforms to the shape of the suture leader.
 5. Thesuture guide assembly of claim 3 wherein the first shell opening has adimension that is smaller than the dimension of the widest portion ofthe suture leader.
 6. The suture guide assembly of claim 5 wherein thefirst shell opening is configured such that when the guide tool is movedfrom the open position to the closed position, the conical tip of thesuture leader is driven through the first shell opening, and isprevented from being retracted from the shell via the first shellopening.
 7. The suture guide assembly of claim 1, wherein the first andsecond arms are angled.
 8. The suture guide assembly of claim 7, whereinthe angle is between 90-180 degrees.